The present invention relates to a selectively insulated dome switch that provides an integral insulative layer bonded to the switch during the manufacturing process, and to a method of manufacturing the same. More specifically, the present invention relates to a metallic dome switch having an integral layer of insulation bonded thereto with precisely located openings to allow proper operation of the switch.
Currently, dome switches are manufactured as follows: sheets or strips of thin metal, generally stainless steel, are fed through a press where the raised profile dome is first formed, and then the dome is stamped out of the carrier material to form a stand alone contact switch component. The dome switches produced using this method are all metallic and are completely conductive. To use a dome switch of this type in an electronic device, an additional layer of insulating material, such as an insulation disc or pad, must be installed under the dome switch to prevent unwanted electrical contact when the switch is in the normal convex resting position.
The difficulty that arises with the current state of the art is primarily related to integration of the switch with other components and insulation of the switch from the other components. To employ a dome switch, as described herein, a second layer of insulating material must be also installed in the device to isolate the switch from the other circuitry in the device. For example, in a flashlight application, a dome switch may be installed adjacent to a terminal of a coin type battery. In the normal resting state, the outer peripheral edges of the dome switch must be electrically isolated from the battery terminal to prevent the flow of electricity. This requires an insulated pad to be positioned between the switch and the battery terminal. However to allow actuation, a hole must be provided in the isolation material so that when the dome is depressed and inverted, the center of the dome can contact the battery terminal and close the circuit. This separate layer of insulating material thus increases manufacturing time and cost. In addition, because of the way the dome switch functions, the opening that is provided in the insulation material must accurately correspond to the center of the dome to allow only the center of the dome to make electrical contact with the battery when the dome is depressed. Therefore, the insulative layer must be properly aligned with the dome when installed to allow proper functioning of the switch.
Insulated dome switches have been known in the prior art. In this regard, it has been known to manually place domes on a magnetic fixture in orientation with each other and apply an adhesive backed laminate sheet, whereby the fixture establishes the spacing between and orientation of the domes as the sheet is applied. The term domes, sometimes called dome switches, as used in this application refers to domes having a convexo-concave shape and an outer periphery that may be circular, circular with a single flat tab, circular with a plurality of flat tabs, or otherwise shaped. More particularly, the domes referred to herein are metal and are stamped from a suitable metal strip and are also of a type that would require orientation. Further, the dome switches referred to herein generally include a layer of insulation that is applied during the manufacturing process to create a switch that functions properly in the device into which it is installed.
It is also known in the prior art to form laminated dome switches by stamping domes and inserting them in oriented fashion into pockets of a continuous tape. To maintain their orientation in the tape, a cover is placed on the tape and the assembled cover and tape is wound on a spool or reel. The assembly may be later removed for purposes of applying the domes into the finished product such as a keyboard. The laminate cover may be in the form of a releasable liner or strip of plastic that would maintain the domes in place in the pockets. This type of a system is called a pocket-tape system.
It has also been known to make a continuous strip of domes by stamping the domes one at a time using a punch press or stamping machine and directly applying the domes to the adhesive side of a dome seal. Thereafter, the domes are covered with a backup strip or release liner before being wound on a reel. Additionally, these single domes may be arranged for individual removal from the backup strip by kiss-cutting the dome seal.
In all of the prior art dome switches, the laminate is applied to one side of the dome and the other side is left exposed. In this manner, the exposed metallic side of the dome is used for electrical contact. In prior art applications, the peripheral edge of the dome generally sits on one electrical contact point and a second contact point is located centrally beneath the dome. When the dome is compressed, the center of the dome makes contact with second central contact point thus energizing the circuit. With the advent of a demand for greater efficiency, lower cost and smaller components in electronics packages, there is a demand for a dome switch that has an integrally formed insulative layer that selectively controls the contact points of the switch thereby eliminating the need for installing a separate insulative component.
The present invention provides for a unique and novel dome switch construction that includes an integral insulative layer that is precisely cut and aligned with the dome switch mechanism during fabrication. In this manner, the additional assembly step previously required for placement of the insulative layer is eliminated, while also reducing the potential for malfunctions due to improper alignment between the switch and the insulating material. Prior to feeding the metal sheet stock or strip stock into the equipment for stamping, a die cut layer of film is applied to one side of the sheet or strip. The film is precut into the shape of the desired insulative layer in the finished switch product. The film may be formed from a variety of materials known in the art to have insulating properties be dielectric such as Mylar or elastomeric rubber and may take the form of a tape with preapplied adhesive or a sheet to which an adhesive is applied prior to laminating with the metallic switch stock.
Prior to lamination with the metallic switch feed stock, the film material is die cut so as to have both index markings and periodic openings that correspond to the areas of the dome switch that are required to be uncovered both to provide electrical conductivity as a part of the proper function of the switch and in the areas of waste around the periphery of the switch to be stamped. The metallic feed stock also has index markings for alignment of the film layer with the metal stock and registration of the laminated material in the stamping machine. This registration is necessary to insure that when the dome switches are stamped from the laminated material the periodic openings in the film fall in the proper locations on the finished product. The sheet of metal including the laminate film is then cooled to a temperature near freezing to facilitate clean stamping of the laminated feedstock during the stamping process and is then fed into the forming and cutting press. The step of cooling the sheet is an important aspect of the present invention in that it prevents the film layer and adhesive from adhering to the cutting dies and gumming up the equipment. When feeding the laminated and cooled stock into the press, the stock is aligned using the registration marks and the dome is formed and then cut out of the carrier material.
It is therefore an object of the present invention to provide an improved integrally insulated dome switch having precise operational alignment while eliminating additional assembly steps and potential human assembly errors from the finished product. It is also an object of the present invention to provide a dome switch for use in electronic devices that eliminates the need for additional insulative components thereby reducing the space required for the overall assembly. It is still a further object of the present invention to provide a method of manufacturing a dome switch with an improved integrally formed selective insulation layer.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.